In hopes to boost its profits amid cheaper competition, Sepracor has entered into a marketing deal with GlaxoSmithKline to market its sleep drug Lunesta outside North America.

Under terms of the deal, Sepracor will receive an initial payment of $20 million, plus additional milestone payments, reaching up to $155 million.

Lunesta’s US sales have slowed since this spring when cheaper generic copies of Sanofi-Aventis’ rival sleeping pill Ambien were made available.

Lunesta was approved in 2005 and had US sales of approximately $567 million last year.

Lunesta will be marketed under the brand name Lunivia in Europe and Japan. The drug is expected to be approved in Europe, where the insomnia market is estimated to be at $500 million, by the second half of 2008, Sepracor and GSK said.

Lunivia has the potential for authorization in as many as 27 EU member countries, the drugmakers said.